1. Field of the Invention
This invention relates to electrochemical devices, and more particularly, to electrolytic tilt sensors.
2. Description of the Related Art
Electrolytic tilt sensors include devices that provide an output voltage proportional to tilt angle and a phase indicative of tilt direction when configured as part of an appropriate electrical circuit. Tilt sensors, originally conceived for weapons delivery and aircraft navigation, are presently used in applications such as oil rig leveling and bore angling, construction laser systems, automotive wheel alignment, seismic and geophysical monitoring, and virtual reality systems.
An electrolytic tilt sensor is typically comprised of a glass envelope or housing that is partially filled with an electrolytic solution and a plurality of conductive electrodes (including one common electrode) which are partially immersed in the electrolytic solution. A portion of the cell which remains unfilled defines a gaseous bubble, which shifts as the cell is tilted, also causing the electrolyte to shift. Consequently, the electrodes become more or less immersed by the electrolyte as the bubble shifts. This shift provides a change in impedance between any one electrode and the common electrode. When the tilt sensor electrodes are configured as part of an appropriate electrical circuit, the angle of tilt may be correlated to an output voltage of the circuit.
The geometric configuration of the enclosure and the arrangement and shape of the electrodes effects the quality and performance of each tilt sensing device. Moreover, the construction of the device directly effects the linearity of its output signal. Various geometric configurations of devices have been disclosed in the prior art, for example, U.S. Pat. No. 2,713,726 discloses a rectangular enclosure; U.S. Pat. No. 3,487,303 discloses a spherical housing; U.S. Pat. No. 3,823,486 discloses a housing having a toroidal configuration; and U.S. Pat. No. 5,170,567 discloses a cylindrical housing.
The spherical device described in U.S. Pat. No. 3,487,303 has a glass housing that consists of two hemispherical portions which are sealed together to form a unitary sphere. Two rectangular electrodes are embedded in the walls of the hemispherical sections and are disposed in diametrical opposition. Another electrode is suspended in the lower portion of the sphere by a plurality of legs which are connected by a ring that is embedded in the wall of the glass enclosure. In a steady upright position, one half of each of the two embedded electrodes are immersed in solution, and the suspended electrode is completely immersed. This geometry provides constant length electrical paths between the electrodes irrespective of the orientation of the device. Consequently, the output potential of the device will be substantially linear. Although the configuration of this device provides advantages over other prior art tilt sensors, it is extremely difficult to fabricate at a low cost. Therefore, it is an object of the subject invention to provide a low cost tilt sensor with improved accuracy and linearity.